The application relates to a sensor unit for activating a blocking mechanism for a belt retractor of a motor vehicle.
Such a sensor unit comprises a sensor element of a certain mass; a receptacle in which the sensor element is displaceably mounted; as well as a coupling mechanism coupling the sensor element with a blocking mechanism assigned to the belt retractor so that the blocking mechanism can be activated by a displacement of the sensor element in the receptacle via the coupling mechanism and thereby blocks a displacement of the belt retractor.
In such a sensor unit the sensor element, due to its mass under normal operating conditions of the motor vehicle, is kept in a defined position within the assigned receptacle of the sensor unit by gravity acting upon the sensor element. However, if accelerating forces act upon the sensor element transversally to gravity caused by a deceleration of the vehicle for instance as a result of strong braking action of the motor vehicle or in the case of a crash, the sensor element being in the receptacle is displaced out of its resting position and acts upon the coupling mechanism arranged downstream of the sensor element in such a manner that the blocking mechanism assigned to the belt retractor is activated. Through this, the belt retractor is blocked for further (rotational) displacement so that a safety belt of the motor vehicle assigned to the belt retractor is hindered in a further belt pullout, so that a vehicle occupant using the safety belt is kept in its vehicle seat in a safely manner.
The sensor element in such a sensor unit is typically formed as a metallic ball and the receptacle assigned to it usually consists of plastics with (calotte) areas for mounting the ball. However, also other constructional systems are conceivable as long as it is guaranteed that the sensor element (which is kept practically in a rest position by gravity under normal operating conditions of a motor vehicle) is displaced or deflected in such a manner in case of a vehicle deceleration exceeding a certain level that the blocking mechanism of the belt retractor is activated by the coupling mechanism arranged downstream of the sensor element and thereby the belt retractor is blocked.
The bearing surfaces of the receptacle are formed for instance by an appropriate selection of material and/or by polishing in such a manner that an easy displacement of the sensor element especially a sensor ball is facilitated by forces acting transversally to weight.
Such sensor units (also called vehicle sensitive sensor units) have to be protected from contamination specifically by (viscous) liquid substances which could lead to an adhesion of the sensor element to its assigned inner surface of the receptacle. Because by this the activation of the blocking mechanism would be delayed so that a larger belt pullout would result until the belt retractor can be blocked.